Seawater intrusion modeling in the Metaponto coastal aquifer (Basilicata, southern Italy).

The present study aims to model the seawater intrusion (SWI) in the Metaponto coastal plain (Basilicata region, southern Italy) by analysing the geological, hydrogeological, and hydrochemical features of the aquifer system and external factors such as excessive withdrawals and climate change. In the study area, groundwater supplies are crucial for agricultural and economic growth. The Metaponto coastal plain is a relevant area for the region development due to the touristic and intensive agriculture sectors. Different anthropogenic impacts play a significant role in facilitating the SWI process in addition to the effects of climate change. In the last century, the Irrigation and Land Development Authority’s hydraulic arrangement and land reclamation works of the marshy areas have aided the development of the plain. Groundwater exploitation to support agriculture, tourism, and industrial activity, as well as the effects of climate change causing modifications in the recharge process, have strongly impacted the hydrogeological conditions of the aquifers in the whole plain, intensifying the potential SWI that must be considered relevant in this coastal system. Nowadays, groundwater resources are exposed to quantitative degradation due to the historically unfavourable climatic conditions worsened by climate change and the growing water demand, and to qualitative degradation also caused by the SWI. The effective infiltration rate of the area is moderate due to the Mediterranean climate conditions, characterized by high temperatures and scarce precipitation concentrated mainly in winter. Based on the outcomes of different studies conducted in the study area, such as hydrogeological and hydrochemical investigations, and the intrinsic vulnerability to SWI assessment, numerical simulations were carried out in this work for the portion of the coastal plain more susceptible to SWI. The geological, hydrogeological, hydrological, climatic, and hydrochemical data collected and processed were employed to define the aquifer conceptual model, which was the first step for the following numerical simulations of groundwater flow and the modeling of the SWI phenomenon. To evaluate and model the SWI process in the most prone area of the Metaponto coastal plain, groundwater flow and variable-density transport, under steady-state and transient conditions, were simulated with MODFLOW and SEAWAT codes integrated into Visual MODFLOW Flex 7.0 software (© 2021 by Waterloo Hydrogeologic). A three-dimensional groundwater flow numerical model was developed, and water table and groundwater salinity variations were simulated starting from the hydrogeological conceptual model of the coastal aquifer. The pumping rates effects and the climate change impact on the aquifer recharge were considered in different scenario simulations. Considering the climate change scenario on direct recharge assessment, no significant changes to the SWI phenomenon result. On the contrary, higher groundwater pumping discharges appear to influence the inland progression of brackish water. The results highlighted that the SWI is potentially not negligible in the future under wells exploitation and may impact the groundwater SWI level risk. The numerical modeling outcomes presented in this work can support groundwater quality and quantity protection and provide indications for implementing management criteria and strategies addressing climate change and variations in water demand.